Dr Bubar is ice skating as part of a new educational show he is creating called
ID: 1417807 • Letter: D
Question
Dr Bubar is ice skating as part of a new educational show he is creating called “Physics on Ice”. As part of the show he skates to the exact middle of the skating rink with a bag of 5 tennis balls and a tennis ball gun. He shoots the tennis balls away from him. Each tennis ball has a mass of 60 grams and travels out of the end of the gun at a velocity of 30 m/s. Dr Bubar has a mass of 70 kg. a) What recoil speed does Dr Bubar acquire? b) The coefficient of kinetic friction between the ice and Dr Bubar’s skates is 0.10. This is the only force acting. Using part “a” and the above information, how far does Dr Bubar skid?
Explanation / Answer
conservation of linear momentum
m = mass of tennis ball, M = mass of Dr Bubar
0 = mv + MV
=> V = -mv/M = 0.06 * 30 / 70 = 0.026m/s
deceleration due to friction = mu * g = 0.1 * 10 = 1m/s^2
=> v^2 - u^2 = 2*a*S
=> -6.6 e-4 = -2 * 1 * s
=> S = 0.33mm
He shoots balls 5 times, hence total skidding distance = 5 * 0.33 = 1.65mm
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